The invention relates to apparatus and method for storing a data stream of moving images and voices into a memory device such as a magnetic disk unit or the like and for supplying the stream in accordance with a request from the outside and, more particularly, to apparatus and method for efficiently processing an input/output request of a data stream of different speeds designated.
Hitherto, as stream processing systems for continuously supplying a large amount of data as a data stream, for example, there are a video on-demand system, a multimedia data base, a desk-top presentation system, and the like. Such a stream processing system is ordinarily constructed by an input/output device for communicating with the outside, a memory device such as a magnetic disk device or the like, and further a buffer memory. In the video on-demand system or the like, since a data stream of moving images and voices is supplied and the user requests various speeds of the stream, it is important to accept a plurality of stream requests of different speeds and to efficiently process them. Even in case of handling only a text such as relational data base, in the case where a large amount of data such as a decision support data base is read and processed and the result is written out, pipeline-like processes are effective. In this case, if a supplying speed of the stream to the outside can be designated in accordance with the processing contents, a buffer memory can be effectively used.
In the conventional system, when there is a request for streams of different speeds, a time-dependent schedule regarding the uses of a memory device, a buffer memory, and an input/output device is formed from a list of un-used resources. The stream is supplied in accordance with the schedule formed. However, such a conventional stream processing system has the following problems. First, when a schedule is formed every request, it takes a time for scheduling, resulting in a decrease in response speed. In case of forming a schedule every request, a vain resource occurs in the resources, and there is a possibility of a decrease in number of streams which can be simultaneously supplied. Further, whether the apparatus can meet a new request or not cannot be known unless a schedule is formed. Therefore, a time until a busy is responded to a request which cannot be satisfied becomes long.